Microstructure and Shear Strength of SiC Joints Brazed with a Si-Ti-Al Filler Alloy

The joining of solid-state sintered silicon carbide (SiC) was achieved using a novel Si-Ti-Al ternary alloy via vacuum brazing. This study investigates a predominantly non-carbide-dominated interfacial bonding mechanism and the influence of brazing temperature on joint microstructure, mechanical properties, and high temperature reliability. The high Si content promoted the incorporation of Ti into Ti-Si phases within the brazed seam, thereby limiting the amount of Ti available for reaction with SiC. No continuous TiC layer was detected within the spatial resolution of the employed characterization methods. Minor discrete Al₄C₃ precipitates were identified at the interface but did not constitute the dominant bonding phase. Brazing at 1360 °C yielded an optimal microstructure featuring highly regular coral-like eutectic clusters, resulting in a peak room temperature shear strength of 102.8 MPa. The joints also exhibited favorable high temperature reliability, maintaining a shear strength of 58.4 MPa at 1000 °C. Microstructural analysis following thermal exposure revealed partial coarsening of primary blocky phases and interfacial Al₄C₃ precipitates via Ostwald ripening, which contributed to the reduction in high temperature strength. Nevertheless, the robust retention of fine eutectic clusters ensured satisfactory structural stability under thermal loading. This work provides a viable strategy for designing Si-based brazing fillers for high-performance SiC ceramic joining.